Cancer of the human esophagus and lung represents a major cause of death in certain populations of people throughout the world. In focusing our efforts on these two organ systems, we have initially evaluated the usefulness of analysis of keratin protein patterns and cross-linked envelopes in the characterization of epithelial neoplasms. Distinctive qualitative and quantitative differences in the spectrum of keratin proteins were found in the carcinomas compared with their nontransformed counterparts. Analysis of keratin protein patterns appeared to be a useful adjunct in defining the type of tumor present. Moreover, assessment of cross-linked envelope-forming capabilities served as a specific marker for squamous differentiation, and the extent of envelope formation correlated well with the degree of squamous differentiation. The tumor with more well-differentiated squamous carcinomas formed more cross-linked envelopes. We have established human esophageal and lung carcinoma cell lines in cell culture to evaluate if their properties in vitro faithfully manifest those of the original tumor, thereby representing useful models of carcinogenesis in vitro. Moreover, we have compared the growth and differentiated properties of these carcinoma cells with their nontransformed counterparts. Numerous morphological and biochemical differences were observed between normal and malignant epithelial cells in culture. Significant changes in the array of keratins and in the proportions of cells making cross-linked envelopes were noted. The results we obtained paralleled findings with tumor masses indicating that the tumor cells in cell culture continue to maintain a program of gene expression reflective of that of the original tumor.